This invention relates to the use of water ballast as a stabilizing force on a sailboat. Many new high performance racing and cruising sailboats are being manufactured with built-in rigid internal water ballast tanks to improve their upwind performance, without sacrificing downwind performance. This is accomplished by filling the windward ballast tank with water while going upwind to stabilize the sailboat, and emptying the ballast when going downwind for less weight. Examples of internal water ballast being used in new high performance cruising sailboats can be found in CRUISING WORLD magazine articles in June 1997, on page 91, and in August 1998, on page 36.
Water ballast simply works by reducing the angle of heel on a sailboat. It makes the keel, rudder and sails increase their lift in the horizontal direction, which generates greater driving and tracking forces that make the sailboat go faster. Although there is additional drag from the hull with the added ballast weight, it is minimal when compared to the gain. Most modern sailboats are light and have flatter under bodies which are capable of going beyond their normal hull speed while planing. Speeds beyond hull speed are generally achieved going down wind in brisk conditions having good driving force, when the sailboat's bottom sections are kept flat on the water for planing. The driving forces on a reach or upwind are not as direct, which makes the sailboat heel and the flat bottom sections are not longer being presented. Adding water ballast on the windward beam while on a reach reduces the heeling angle, which again presents a flatter bottom for planing and increases the driving forces which makes the sailboat go faster.
Light modern cruising sailboats also tend to have a harsh motion in heavy seas. This can make it uncomfortable and difficult to perform normal tasks on ocean passages, with excessive heeling only aggravating the situation. By adding additional water ballast weight on the windward beam, rolling and tossing are dampened and more velocity is sustained through oncoming waves. With slower and less internal movement, as well as angle of heel, one has a more comfortable and safer sea kindly ride in heavy seas, with less time spent at sea with the added speed. Also, water ballast can be placed on both sides of the sailboat to reduce rolling at anchorage.
Unfortunately, any attempt to add internal water ballast to sailboats without preexisting ballast tanks would require major reconstruction and would not be practical or cost effective, and the internal tanks would take up valuable space.